Major League Soccer set a new high-water mark for average attendance this season, as expansion clubs in Portland and Vancouver lived up to preseason expectations for big crowds, and a new stadium and rebranding effort in Kansas City turned around that city’s once-ailing club.

Average attendance for the 18 clubs rose 7.2 percent to 17,872 spectators a game this season, surpassing the league’s previous record of 17,406, which was set during its inaugural season in 1996. The league’s lowest attendance came in 2000 when it averaged just 13,756 fans. Since 2007, its average has consistently stayed between 16,000 and 17,000. The strong showing at the gate brought MLS’s average above the most recent seasons for both the NHL (17,132) and NBA (17,323).

“It’s historic for us — we exceeded our best with 18 teams, and we only had 10 back then,” said MLS President Mark Abbott. “We have Montreal joining next year, and we believe that we will have a very positive story in that market as well.”

The Seattle Sounders again led the league with a whopping average attendance of 38,496, 15,000 fans more per game than the next closest franchise. Evidence of the strength of the team’s appeal is that if one took the Sounders out of the MLS mix, the league would have averaged more than 1,000 fans fewer per game, at 16,659.

With the Sounders jumping to the top of MLS’s attendance rankings upon their debut in 2009, league officials expected the expansion Vancouver Whitecaps and Portland Timbers to also score big numbers this season, as both teams own 20-plus ears of history in the Division II USL and old Division I NASL leagues, much like the Sounders. The teams did not disappoint, as Portland sold out all 17 home games and Vancouver sold out seven matches on its way to reaching 97.2 percent capacity.

The demand for tickets in Portland prompted Timbers officials to build temporary seating at Jeld-Wen Field for two of its last three games to expand capacity from 18,827 to 20,323. The team easily sold the additional seats, and this offseason the Timbers will permanently install seating to bring the stadium’s capacity to 23,000, and increase the season-ticket cap from 12,500 to 14,500.

Sporting Kansas City, which dropped its original name “Wizards” in December 2010 in favor of a more European name and brand, also posted impressive attendance statistics, selling out nine home games and 96.4 percent of its total ticket inventory. The club undoubtedly was helped by its new $200 million Livestrong Sporting Park, though the club had to play all 17 of its home games during the second half of the season because the park didn’t open until June.

“Half of our games were on school nights because we were so backloaded,” said a team representative. “Next year we will have more Saturday night games.”

The club previously averaged 10,006 at CommunityAmerica Ballpark, and its average this season was 17,810.

Of the league’s 16 non-expansion teams, 12 showed either gains or flat attendance. Toronto FC saw its numbers shrink by 0.9 percent. However, the club is still selling at 101.3 percent of capacity. The Chicago Fire saw a 9.7 percent dip in average attendance. The Columbus Crew saw the largest drop, a 16.8 percent decrease in attendance.

Mike Malo, senior vice president for sales and marketing with the Crew, said the team has lowered the price of season tickets for 2012 by as much as 33 percent in an attempt to reverse the slide. The Crew announced the new prices in a campaign to reach 10,000 season-ticket holders, called “Goal 10K.” Malo said the team is currently at 4,900 new and renewed tickets for 2012.

The league’s gate numbers were mirrored by growth in television audiences, although MLS still trails the other major professional leagues in viewership. For its 26 matches on ESPN and ESPN2, MLS stayed at a 0.1 rating, but its audience grew to 321,000 viewers, up 15 percent from 2010. On Fox Soccer, the average viewership grew 34 percent to 75,000, and on Fox Deportes, audiences grew 53 percent to 29,000, which translated to a 0.31 rating.

Abbott said the league is in talks with its new television partner NBC to finalize a weekly broadcast schedule for 2012.